In order to improve the reliability of the correct decoding of a wrong data block, the wireless communication system usually employs the Hybrid Automatic Repeat Request (HARQ) technology. The HARQ is realized by combining the Automatic Repeat Request (ARQ) and the Forward Error Correction (FEC). At the receiving end, it is firstly judged whether the data block is correctly received through a Cyclic Redundancy Check (CRC); and if an error occurs, the ARQ will be sent to request a data retransmission. Such HARQ technology is employed in the LTE and LTE-Advanced uplink system. The base station (NB or eNB) detects the CRC, and sends a repeat request to the user equipment when an error is found. Then the user equipment retransmits the data block to the base station after receiving the request.
In the LTE-Advanced (LTE-A) system, in order to improve the uplink peek rate, a Multiple Input Multiple Output (MIMO) technology is introduced. The user equipment may be provided with up to four transmitting antennas. The precoding technology is a branch of the MIMO technology, i.e., each data stream is simultaneously transmitted in respective transmitting antennas after being multiplied by the precoding matrix. In the LTE-Advanced system, the precoding matrix for initial transmission (herein also referred to as initial transmission precoding matrix) has been determined, as shown in Tables 1 to 4. The rank is the number of the data streams, e.g., when there are 3 data streams, the rank is 3. Herein the number of data streams for initial transmission is referred to as the rank for initial transmission (initial transmission rank), and the number of data streams for retransmission is referred to as the rank for retransmission (retransmission rank).
Since the channel fadings experienced by the data streams are not completely the same, in the initial transmission, there may be a condition that the data corresponding to some data streams are correctly received, while the data corresponding to other data streams are wrongly received. In order to improve the transmission efficiency, only the wrong data streams are retransmitted, and the retransmission rank may be less than the initial transmission rank. The minimum unit of the retransmission is the transmission block (TB). FIG. 1 illustrates a mapping relationship between TBs and data streams. As illustrated in FIG. 1(a), two transmission blocks are transmitted in two layers (Layer 1 and Layer 2) respectively. If there is only one TB not successfully decoded, (NACK, ACK) or (ACK, NACK) will be returned to the data sender. This only needs to transmit the TB under NACK, i.e., retransmission rank (1) is different from (lower than) retransmission rank (2). Similarly, as illustrated in FIG. 1(b), the first TB of the two TBs is transmitted in Layer 1, and the second TB is transmitted in Layers 2 and 3. If there is only one TB not successfully decoded, (NACK, ACK) or (ACK, NACK) will be returned to the data sender. This only needs to transmit the TB under NACK, i.e., the first TB is retransmitted with a retransmission rank of 1 when (NACK, ACK) is received, the second TB is retransmitted with a retransmission rank of 2 when (ACK, NACK) is received, while the retransmission ranks are both different from (lower than) the initial transmission rank (3). As illustrated in FIG. 1(c), the first TB of the two TBs is transmitted in Layers 1 and 2, and the second TB is transmitted in Layers 3 and 4. If there is only one TB not successfully decoded, (NACK, ACK) or (ACK, NACK) will be returned to the data sender. This only needs to transmit the TB under NACK, i.e., the first TB is retransmitted with a retransmission rank of 2 when (NACK, ACK) is received, the second TB is retransmitted with a retransmission rank also of 2 when (ACK, NACK) is received, while the retransmission ranks are both different from (lower than) the initial transmission rank (4).
How to select the precoding matrix during the retransmission is a problem urgently to be solved. In the conventional art, the precoding matrix for retransmission (herein also referred to as retransmission precoding matrix) is obtained by performing a certain algorithm on the precoding matrix for initial transmission. For example, international patent publication No. WO2010/024645 discloses that a precoding matrix for retransmission is generated by multiplexing a precoding matrix for initial transmission with a unary matrix, and international patent publication No. WO2010/015640 discloses that a precoding matrix for retransmission is generated using time correction channels.
During the study of embodiments herein, the inventor finds that in the above technical solutions of the conventional art, the condition that the retransmission rank and the initial transmission rank are different from each other is not considered. In addition, a precoding matrix different from those included in the existing code book shall be generated, which requires more memory spaces of the sender and the receiver.
To be noted, the above introduction to the background art is just made for the convenience of clearly and completely describing the technical solution of the present invention, and to facilitate the understanding of a person skilled in the art. It shall not be deemed that those technical solutions are well known to a person skilled in the art just because they are described the Background section of the present invention.
TABLE 1Precoding Matrix with the Rank of 1Code bookIndexes 0-7      1    2    ⁡      [                            1                                      1                                      1                                                  -            1                                ]        1    2    ⁡      [                            1                                      1                                      j                                      j                      ]        1    2    ⁡      [                            1                                      1                                                  -            1                                                1                      ]        1    2    ⁡      [                            1                                      1                                                  -            j                                                            -            j                                ]         1    2    ⁡      [                            1                                      j                                      1                                      j                      ]        1    2    ⁡      [                            1                                      j                                      j                                      1                      ]        1    2    ⁡      [                            1                                      j                                                  -            1                                                            -            j                                ]        1    2    ⁡      [                            1                                      j                                                  -            j                                                            -            1                                ]   Indexes 8-15      1    2    ⁡      [                            1                                                  -            1                                                1                                      1                      ]        1    2    ⁡      [                            1                                                  -            1                                                j                                                  -            j                                ]        1    2    ⁡      [                            1                                                  -            1                                                            -            1                                                            -            1                                ]        1    2    ⁡      [                            1                                                  -            1                                                            -            j                                                j                      ]         1    2    ⁡      [                            1                                                  -            j                                                1                                                  -            j                                ]        1    2    ⁡      [                            1                                                  -            j                                                j                                                  -            1                                ]        1    2    ⁡      [                            1                                                  -            j                                                            -            1                                                j                      ]        1    2    ⁡      [                            1                                                  -            j                                                            -            j                                                1                      ]   Indexes 16-23      1    2    ⁡      [                            1                                      0                                      1                                      0                      ]        1    2    ⁡      [                            1                                      0                                                  -            1                                                0                      ]        1    2    ⁡      [                            1                                      0                                      j                                      0                      ]        1    2    ⁡      [                            1                                      0                                                  -            j                                                0                      ]         1    2    ⁡      [                            0                                      1                                      0                                      1                      ]        1    2    ⁡      [                            0                                      1                                      0                                                  -            1                                ]        1    2    ⁡      [                            0                                      1                                      0                                      j                      ]        1    2    ⁡      [                            0                                      1                                      0                                                  -            j                                ]  
TABLE 2Precoding Matrix with the Rank of 2Code bookIndexes 0-7      1    2    ⁡      [                            1                          0                                      1                          0                                      0                          1                                      0                                      -            j                                ]        1    2    ⁡      [                            1                          0                                      1                          0                                      0                          1                                      0                          j                      ]        1    2    ⁡      [                            1                          0                                                  -            j                                    0                                      0                          1                                      0                          1                      ]        1    2    ⁡      [                            1                          0                                                  -            j                                    0                                      0                          1                                      0                                      -            1                                ]         1    2    ⁡      [                            1                          0                                                  -            1                                    0                                      0                          1                                      0                                      -            j                                ]        1    2    ⁡      [                            1                          0                                                  -            1                                    0                                      0                          1                                      0                          j                      ]        1    2    ⁡      [                            1                          0                                      j                          0                                      0                          1                                      0                          1                      ]        1    2    ⁡      [                            1                          0                                      j                          0                                      0                          1                                      0                                      -            1                                ]   Indexes 8-15      1    2    ⁡      [                            1                          0                                      0                          1                                      1                          0                                      0                          1                      ]        1    2    ⁡      [                            1                          0                                      0                          1                                      1                          0                                      0                                      -            1                                ]        1    2    ⁡      [                            1                          0                                      0                          1                                                  -            1                                    0                                      0                          1                      ]        1    2    ⁡      [                            1                          0                                      0                          1                                                  -            1                                    0                                      0                                      -            1                                ]         1    2    ⁡      [                            1                          0                                      0                          1                                      0                          1                                      1                          0                      ]        1    2    ⁡      [                            1                          0                                      0                          1                                      0                                      -            1                                                1                          0                      ]        1    2    ⁡      [                            1                          0                                      0                          1                                      0                          1                                                  -            1                                    0                      ]        1    2    ⁡      [                            1                          0                                      0                          1                                      0                                      -            1                                                            -            1                                    0                      ]  
TABLE 3Precoding Matrix with the Rank 3  0-3       1    2    ⁡      [                            1                          0                          0                                      1                          0                          0                                      0                          1                          0                                      0                          0                          1                      ]        1    2    ⁡      [                            1                          0                          0                                                  -            1                                    0                          0                                      0                          1                          0                                      0                          0                          1                      ]        1    2    ⁡      [                            1                          0                          0                                      0                          1                          0                                      1                          0                          0                                      0                          0                          1                      ]        1    2    ⁡      [                            1                          0                          0                                      0                          1                          0                                                  -            1                                    0                          0                                      0                          0                          1                      ]     4-7       1    2    ⁡      [                            1                          0                          0                                      0                          1                          0                                      0                          0                          1                                      1                          0                          0                      ]        1    2    ⁡      [                            1                          0                          0                                      0                          1                          0                                      0                          0                          1                                                  -            1                                    0                          0                      ]        1    2    ⁡      [                            0                          1                          0                                      1                          0                          0                                      1                          0                          0                                      0                          0                          1                      ]        1    2    ⁡      [                            0                          1                          0                                      1                          0                          0                                                  -            1                                    0                          0                                      0                          0                          1                      ]     8-11      1    2    ⁡      [                            0                          1                          0                                      1                          0                          0                                      0                          0                          1                                      1                          0                          0                      ]        1    2    ⁡      [                            0                          1                          0                                      1                          0                          0                                      0                          0                          1                                                  -            1                                    0                          0                      ]        1    2    ⁡      [                            0                          1                          0                                      0                          0                          1                                      1                          0                          0                                      1                          0                          0                      ]        1    2    ⁡      [                            0                          1                          0                                      0                          0                          1                                      1                          0                          0                                                  -            1                                    0                          0                      ]    : Indexes
TABLE 4Precoding Matrix with the Rank of 4Code bookIndex 0      1    2    ⁡      [                            1                          0                          0                          0                                      0                          1                          0                          0                                      0                          0                          1                          0                                      0                          0                          0                          1                      ]  